This invention relates generally to a method and apparatus for maintaining the external surface of a tubular member free of scale, deposits, and the like. This invention is particularly suited to the scraping and cleaning of protective quartz tubes used in the ultra-violet sterilisation and/or disinfection of water and other liquids, but is not limited thereto.
It is well known to use ultraviolet light in the sterilisation and/or disinfection of water. In addition, ultraviolet light may be used to effect other treatments or reactions in fluids, including water and air. The ultraviolet light is typically obtained from a lamp that is in the form of a straight hollow tube of a material transparent to ultraviolet light, especially a quartz tube. A quartz sheath may also be used. Electrical connections extend through the sealed ends of the tubes, and these electrical connections are protected from contact with the fluid.
The surface of the ultraviolet lamp, or outer sheath if used, tends to accumulate scale, deposits or the like, especially after a period of continuous use. The problems of scale and other deposits are partially acute in the treatment of water. Accumulation of scale and other deposits on the surface of the tube reduces the transmission of ultraviolet light from the lamp into the fluid. This causes a decrease in the intensity of the light and consequently the efficiency and effectiveness of the treatment decreases. In the treatment of water, cleaning of the outer surface of the tube may be required weekly, daily or even more frequently, depending on the quality of the water being treated.
Cleaning of the tubes could be effected by removal of the tubes from the fluid and scraping or chemical treatment. In the typical situation of use of a plurality of tubes in a cluster, this might require partial disassembly of the apparatus and extended down-time in the use of the apparatus.
Various methods have been developed for cleaning of tubes without removal of the tubes from the fluid, using brushes, wipers or the like. One such system is disclosed in U.S. Pat. No. 5,266,280, issued Nov. 30, 1993 to Hallett. In this system, a cylindrical UV-transparent sheath is utilized to isolate a UV lamp from the interior space of a reactor vessel. The sheath is sealed in such a way as to isolate the UV lamp from the fluid. A brush device is provided for brushing the exterior surface of the sheath to remove materials deposited from the fluid. The brush device has at least two brushes with bristles extending radially inwardly towards the sheath as the brushes encompass the sheath. The brushes are coupled together in spaced-apart manner on the sheath with a device for reciprocating the brushes along the exterior of the sheath, preferably on a periodic basis.
U.S. Pat. No. 3,462,597, issued on Aug. 19, 1969 to Young, discloses a UV lamp system for water purification that includes a wiper system for the protective sheath surrounding the UV lamp. The wiper system comprises wiper rings made from Teflon(trademark) or like material not affected by UV radiation. The rings are spaced apart from one another and are preferably split so that they can be elastically or resiliently held on the outside of the protective tube by a spring. The wiping ring is connected to a ring holder which is engaged by a rod that extends through an end of the reactor. The ring holder is then reciprocated to provide a wiping action along the protective tube to remove physical or biological materials that have deposited on the outside of the tube. However, the system would seem to be inadequate to accommodate dimensional variations in the protective tube, which is normally made of quartz. Further, use of wiper rings made of Teflon(trademark) fluoropolymer or similar material would not clean the quartz surface due to a) the lack of a sharp, hard scraping surface (such as a razor) and b) the inherent slipperiness of Teflon fluoropolymer.
U.S. Pat. No. 3,562,520, issued on Feb., 1971 to Hippen, discloses the use of a wiper system to routinely clean a protective quartz tube surrounding a UV lamp. The wiper system includes a number of ring-like wiper elements surrounding and in wiping contact with the external surface of the protective tube. The wiper assembly is urged along the tube by a coil spring. When water to be treated flows through the reactor, the wiper returns to the other end of the tube to effect a wiping of the area of the tube between the inlet and outlet. This is said to ensure that the protective tube is free of deposits during each start-up of the water purifying device.
U.S. Pat. No. 3,904,363, issued on Sep. 9, 1975 to Free, discloses a wiper system that is also activated by water flow. However, for extended continuous water flow, the protective tube would not be cleaned. Water flow moves the wiper system to one end of the tube and keeps it there. When the water shuts off, the wipers descend to the base of the reactor under the influence of gravity. The wiper system includes a flexible semi-rigid plastic or flexible metal membrane. The membrane may be a brush-like textured membrane of composite or plastic material. However, the membrane is very thin and is likely to be inadequate to remove stubborn deposits on the protective sheath. Also, the plastic version of the wiper would be subject to deterioration under a high intensity UV radiation from high powered lamps.
The inability of the devices disclosed in U.S. Pat. Nos. 3,562,520 and 3,904,363 to operate with a continuous flow of water would mean that an extended water flow through the device would result in the gradual build-up of deposits on the protective tube. This would reduce the transmittal of UV light, and consequently the effectiveness of the UV radiation in treating bacteria.
U.S. Pat. No. 5,528,044, issued on Jun. 18, 1996 to Hutchinson discloses use of a wiper assembly having a rod that can be moved from outside the reactor chamber to mechanically reciprocate the wiper assembly. The wiper assembly has a plate with a plurality of radial inwardly extending finger members that engage the outer surface of the tube surrounding the lamp.
Additional patents are U.S. Pat. Nos. 4,482,809, 4,872,980, 5,006,244 and 5,418,370, all issued to Maarschalkerweerd. In the devices described in first three of these patents, the sleeve surrounding the UV lamps becomes periodically fouled with foreign materials, and then requires manual cleaning to remove such materials. The latter patent overcomes this disadvantage by providing a cleaning apparatus which incorporates a cleaning sleeve engaging a portion of the exterior of the radiation source assembly and moveable between a retracted position and an extended position. The cleaning sleeve includes the chamber in contact with part of the radiation source, which chamber is supplied with a cleaning solution suitable to remove undesired materials. Such a method and apparatus for cleaning tends to be relatively complicated and expensive.
A simple and effective method and apparatus for cleaning the exterior surfaces of tubes would be beneficial.
In view of the disadvantages of the prior art enumerated above, it is an object of one aspect of this invention to provide a scraper for removing deposits from the exterior of a tubular member such as a protective quartz sheath.
Accordingly, one aspect of the present invention provides, for the removal of deposits from the exterior of a tubular member, a scraper comprising:
an outer jacket defining an inwardly open circumferential recess and two aligned axial openings,
a scraper element in the form of an elongate resilient wire bent to define a series of integral, concatenated, resilient segments, each pair of adjacent segments being connected through a geniculation,
the geniculations being received within said recess with at least one segment extending substantially along a chord of the aligned axial openings,
whereby, in order to accommodate the tubular member through said aligned axial openings, the tubular member must deform said at least one segment outwardly, so that the resilience of the deformed segment urges it inwardly against the tubular member and causes it to clean the tubular member as the scraper moves axially relative to the tubular member.
A further aspect of the present invention provides a method of removing deposits from the exterior of a tubular member, the method comprising:
providing a scraper which includes:
an outer jacket defining an inwardly open circumferential recess and two aligned axial openings,
and a scraper element in the form of an elongate resilient wire bent to define a series of integral, concatenated, resilient segments, each pair of adjacent segments being connected through a geniculation,
the geniculations being received within said recess with at least one segment extending substantially along a chord of the aligned axial openings,
and inserting the tubular member through said aligned openings so as to deform said at least one segment outwardly, whereby the resilience of the deformed segment urges it inwardly against the tubular member and causes it to clean the tubular member as the scraper moves axially relative to the tubular member.